1. Field of the Invention
The present invention relates to a motor-driven power steering system that makes it possible to prevent a noise or a rattling noise when turning the steering wheel by preventing an inner ring of a tilt bearing from moving in the axial direction of a worm shaft.
2. Description of Related Art
In general, power steering is classified into a type that uses hydraulic pressure of oil and a type that uses power of an electric motor.
The hydraulic power steering is to supply hydraulic pressure, which is made by pumping fluid by a hydraulic pump using power of the engine, in the turning direction of the steering wheel by a driver to help handling, and the motor-driven power steering (hereafter, referred to as MDPS) is to improve a steering force using an electric motor.
According to the MDPS, the electric motor automatically performs control function, depending on the traveling conditions, and accordingly, it can have improved steering performance and steering response as compared with the hydraulic power steering.
Further, the MDPS includes a worm wheel in which a steering shaft is fitted and a worm shaft that is engaged with the worm wheel, and further includes a tilt bearing that optimizes the engagement of the worm wheel and the worm shaft.
However, according to the MDPS in the related art, a dead sound, such as clatter, is made when the steering wheel that has been turned is released while a vehicle is stopped. Further, as the vehicle drives on a rough road or a rugged road, a rattling noise is made by a gap that is generated between the worm wheel and the worm shaft due to a large reaction force that is transmitted from the road surface to the steering shaft.
The above noises are made when the inner ring of the tilt bearing moves in the axial direction of the worm shaft.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.